1. Field of the Invention
This invention relates to the field of alignment controls for self-propelled irrigation systems.
2. Description of the Prior Art
Self-propelled irrigation systems generally comprise an overhead, horizontal distribution pipe made up of a plurality of pipe segments each of which is supported by its own self-propelled tower. The towers have individual drive arrangements which are typically powered by hydraulic fluid or electricity. An essential part of any such self-propelled irrigation system is the alignment control which maintains the pipe segments of the distribution pipe in proper alignment as the irrigation system moves. Typically, an alignment control system comprises a plurality of units positioned at each joint between adjacent pipe segments. Each unit has a sensor for monitoring deflections in the alignment of the adjacent pipe segments and a control vlave operably connected to the sensor which changes the speed of the drive of the nearest tower to the joint in proportion to the sensed deflections. A common mode of operation in self-propelled irrigation systems is to set the drive of one of the pipe segment's tower at a predetermined set speed and have the remaining pipe segments move sequentially in a follow-the-leader, catch up fashion.
Numerous alignment control systems have been patented. Many of these systems use an arrangement of cables to detect deflections of the pipe segments away from a predetermined alignment. Examples of such systems are: U.S. Pat. Nos. 3,599,664 to Hotchkiss et al issued on Aug. 17, 1971 (see FIGS. 5 and 6), 3,394,729 to Bower et al issued on July 30, 1968 (see FIGS. 2 and 8), 3,780,947 to Ririe et al issued on Dec. 25, 1973, 3,352,493 to Curtis issued on Nov. 14, 1967, 3,608,826 to Reinke issued on Sept. 28, 1971 (see FIG. 10), 3,342,417 to Dowd issued on Sept. 19, 1967, 2,893,643 to Gordon issued on July 7, 1959, and 3,353,750 to Dowd issued on Nov. 21, 1967. Such cable systems have been found to have several drawbacks. Notably, the cables cannot be easily and quickly adjusted and any adjustments often require the retying of knots and the replacement of cables. Further, the cables can break, shrink, or stretch during use. Stretching and shrinking can often occur when the temperature and other weather conditions vary while the irrigation system is operating. Even slight stretching or shrinking of the cable or loosening of the cable knots as in a system like that of Hotchkiss (see his FIG. 5) can throw the entire system out of alignment. Also, should it be desireable to run the irrigation system with some pipes in a straight line and others at a considerable angle, cable systems such as Hotchkiss would require that several of the cables be replaced with longer ones and many of the knots retied.
Several alignment control systems use arms which are rigidly attached at one end to one pipe segment and operably attached at the other end to a control valve mounted on the adjacent pipe segment. Examples of these are: U.S. Pat. Nos. 2,628,863 to Maggart issued on Feb. 17, 1953 (see FIG. 6), 3,720,374 to Ross issued on Mar. 13, 1973 (see FIGS. 8-11), 3,386,661 to Olson et al issued on June 4, 1968 (see FIGS. 6-7), and 3,823,730 to Sandstrom et al issued on July 16, 1974 (see FIGS. 3-4). Such systems with rigidly attached arms are often difficult to adjust and difficult to quickly disconnect to avoid damage should the alignment control system malfunction and adjacent pipe segments be placed at a considerable angle to each other. Lever arms which are pivotally mounted near the center of the arm have also been used. In these systems, one end of the lever arm moves with one of the pipe segments and the other end of the lever arm is operably connected to the control valve mounted on the adjacent pipe segment. An example of such a system is U.S. Pat. No. 3,556,405 to Harris et al issued on Jan. 19, 1971 (see FIGS. 24-33).
Other alignment control systems include ones that suspend the pipe segment from a cable like a pendulum and monitor movements of the suspended pipe away from the vertical (U.S. Pat. Nos. 3,353,751 to Dowd issued on Nov. 21, 1967 and 3,314,608 to Curtis et al issued on Apr. 18, 1967). Still others use stress switches (U.S. Pat. No. 3,797,517 to Kircher et al issued Mar. 19, 1974), remotely operated electrical systems (U.S. Pat. No. 3,831,692 to Fry issued on Aug. 24, 1974) and electrical systems which include circuits for specifically pointing out the location of any malfunction (U.S. Pat. No. 3,785,400 to Zimmerer issued on Jan. 15, 1974).
The alignment control system of the present invention is designed to overcome many of the problems experienced in prior art systems. the alignment control system of the present invention is simple, strong, reliable, safe, sensitive to small deflections, and quickly responsive to misalignments. The invention also operates smoothly and can track forwardly and backwardly so that the irrigation system can operate on a reciprocating cycle. Further, the alignment control system of the present invention can be quickly disengaged to avoid damage to it upon a malfunction in the irrigation system and can be quickly and easily adjusted so that adjacent pipe segments can track at any desired relative angle.